Despite the huge advances in processing power …

Delivery route planning remains part art and part science.

Here we've put the art before the science to emphasise that computers are powerful, but they are not exhaustive.

With such computing power at our fingertips it's easy to assume the computer examines every option, and/or knows everything.

Neither are true. And they never will be.

It would take the fastest computer longer to calculate every combination on a 20 drop delivery route than the
driver could drive it. And parcel couriers routinely do 70 drops, not 20.
'Mapping up' takes up to an hour at the beginning of a courier's shift.

"Roadworks on the A14; they might clear by 4:15, and if they don't I'll do Kettering before Wellingborough"
is easier for a human (thank God!) than a computer.

Rather than look at every possible combination, the computer uses
a rule of thumb. The posh name is an 'algorithm'. It's a way of shortcutting
the problem to make it manageable. One such works backwards from the
furthest drop, successively adding deliveries and collections (don't
forget collections!) based on the divert time (or distance, or whatever) from the current route.
We might think of this as a graphical approach, although the distinction isn't nearly so black and white.

The early methods - string round pins on a map - were also graphical

The Dutchman Dijkstra's algorithm is more mathematical.

Whichever approach is used the solution is 'good enough'. It's possible there's a 'perfect' route, but:-

It wouldn't be much better than the good enough route, and

With either graphical or mathematical approaches, it would take longer to find. Could there be a hybrid way,
which combined the two approaches?

I had long pondered this, and the picture shows an early breakthrough.